During the manufacturing of paper, it is often necessary to splice separate sections together in order to maintain a continuous running sheet. Several splices within a paper roll wound for shipment and/or storage is not uncommon. As this continuous sheet is unwound in a printing process, whether for publications or labels, or in another process such as the manufacture of cigarettes, splices must be detected for their removal. This is necessary, not only to avoid process breakdown, but also to prevent splices from appearing in the final product. Splices are especially unacceptable in cigarettes and pharmaceutical labeling.
Greater demands are placed upon splice detection as paper manufacturers are beginning to use repulpable splice materials and adhesives which are necessarily transparent and colorless. Conventional splice detectors, based on optical systems, have historically depended upon opaque markers to indicate their presence. As these markers are unacceptable in paper recycling, other detection methods are being used. These methods employ gamma radiation, ultrasonics, mechanical contact with a moving sheet, and the measurement of abrupt capacitance change between electrodes where the moving sheet acts as a dielectric. All these methods have limitations, especially with materials such as cigarette paper and fine printing paper. A common problem shared by all commercial systems is the need for readjustment to compensate for change from one material type to another, not to mention that needed for changes induced by ambient environment and component aging. Web speed constraints are necessary to prevent web tearing from sensor to web contact and/or web blockage from web flop and vibration within a narrow detector sensing gap.
U.S. Pat. Nos. 4,498,240; 4,314,757; 3,316,760; and 3,577,955 all relate to mechanical methods for splice detection and require some form of physical contact with the moving web. Where these methods might be highly successful with thick, heavy web materials, they would present a threat to cosmetic appearance and tearing to the much lighter sheet materials which are inherently fragile. Should a mechanical device be scaled down to a workable configuration, vibrational movement, inherent in machine running and web movement as compared to that from a typical splice, would be significant enough to trigger false splice signals.
U.S. Pat. No. 2,264,725 utilizes gamma radiation which is transmitted through the moving sheet to measure web thickness and, subsequently, a splice which would be a momentary thickness change. A plurality of sensors is used differentially to compensate for slight variances in material; however, the material must be metallic or dense enough to attenuate the incident gamma radiation to useful levels.
U.S. Pat. No. 4,901,577 describes a device designed for web splice detection in a printing press by measuring abrupt changes in attenuated ultrasonic signals transmitted through the moving sheet. This approach is similar to a light source detector system where light, instead of ultrasonic radiation, is used. In this particular patent, only one sensor system is used with no compensational features for inherent thickness changes within a given product. The comparable light system has been unsuccessful because of false signals being generated, even with continuous manual adjustment.
U.S. Pat. No. 3,432,672 uses light emitter/detector pairs to measure a change in reflection from incident light resulting from logo or a visible marker used to identify a splice. The intent of the disclosed is to eliminate the requirement for a visible identification marker.
U.S. Pat. No. 3,519,922 discloses a device that detects an abrupt thickness change in a moving sheet representing a typical splice. It was particularly designed for sheet materials such as thin papers and uses the material's dielectric properties to induce a proportional capacitance change to a series of electrically charged electrode plates separated by an air gap through which the web splice passes. Since the air gap is a significant portion of the total dielectric, it must be held to a minimum spacing in order for the web dielectric change from a splice to faithfully generate a detection signal. This poses a threat to web travel, especially at high speeds where web flop, especially in a big machine, is significant. Speed constraints would have to be enforced to avoid web tearing. This device uses a plurality of sensors to compare a splice disturbance with a reference, and effectively compensates for the normal web variations within a given product. The patent does express a need for periodic adjustment to "retune" system electronics. This would also be necessary if sensitivity increases were required to monitor thinner than normal sheet materials.
The disclosed overcomes the aforementioned limitations taught in the referenced U.S. patents by making the following unnecessary:
1. Web-to-sensor contact which threatens customer appearance of webs and introduces risk of web breakage.
2. Narrow sensor gap spacing through which a web must pass (U.S. Pat. No. 3,519,922) and the web speed constraints that result.
3. Printed markers, logo, or opaque non-repulpable adhesive for splice identification (U.S. Pat. No. 3,432,672).
4. Appreciable web thickness.
5. Periodic system readjustment to account for different web types, changes in industrial environment, and normal aging of components.
As is known in the art, signals from detected splices can be easily routed to perform a number of various functions besides alarm activation, depending upon specific requirements. The following are typical, but not limited to, examples that could be utilized in the industry.
1. Automatic machine stop (stoppage of web movement). PA0 2. Splice tracking PA0 3. Splice Counting PA0 Splice signals could be counted to hold product within specifications relating to maximum splice occurrence. PA0 4. Identification Marker PA0 A splice signal could activate an edge marker to indicate splice locations. A position encoder could also be used to identify the splice, as it would track the splice and apply edge marking at a specific location on the machine.
A position encoder, mechanically linked to the moving web could be activated by a splice signal. When a predetermined count, representative of a specific splice location, is reached, the splice could be illuminated for observation. Subsequent count settings could decelerate the machine (and web movement) to a complete stop at an exact splice position for its removal, examination, etc. PA1 Two or more independent web systems could be synchronized so that each splice in each web would meet and join at a chosen common point. Position encoders would be used as in the former example, but to the extent of invoking speed/positional changes in each system to make this possible.